Conversion of high-power 15-fs visible pulses to the mid infrared

We measure the efficiency of converting high-power 15-fs $0.8‐\mu \mathrm{m}$ pulses to the mid infrared in GaAs and GaSe as well as the pulse duration and the spectrum of the infrared radiation that is produced. Free-carrier production limits the conversion efficiency in GaAs to approximately $5\times {10}^{-7}$, allowing us to produce 2.5-pJ, 30-fs pulses spanning the spectral range from 6 to $14 \mu \mathrm{m}$. In GaSe we obtain, in a moderately saturated regime, a conversion efficiency of $7.5\times {10}^{-5}$, limited by two-photon absorption, allowing us to produce pulses of 100-fs duration containing 10 nJ of energy.